Central facilities carry out a wide variety of voice and/or data communications with vehicles. These transmissions can be voice communications between a live advisor at the central facility and a vehicle occupant. And these transmissions can also include exchanging data between the central facility and the vehicle. Sometimes, this exchange involves a vehicle that automatically sends data or other information to the central facility. Other times, the central facility may want to ask the vehicle to send it data. In that case, the central facility can send a message to the vehicle (or many vehicles) with a data request. However, these data requests should be sent in such a way that the recipient(s) can be reasonably certain of the sender's identity. Given that central facilities often service a large number of vehicles at the same time in a secure way, it can be challenging to economically and securely send communications to a number vehicles; the wireless transmission cost of doing so can be significant. It would be helpful to wirelessly communicate with vehicles at a reduced cost while maintaining a secure mechanism of carrying out such communications.